Activities with high requirments for hygiene e.g. food industries, hospitals, laboratories etc., are regularly cleaned by different types of sanitizers. The demands on hygiene also lead to is laid stress is laid on the materials which are used as linings in ceilings, walls and floors. The predominant is that only hard, smooth and non-porous materials should be used on surfaces in such rooms. If possible, tiles stainless plate, epoxy paints should be used, but by reason of costs, also simplier indoor paints such as bright latex paints, oil and alkyd paints, etc., are used. These materials are simple to wash from visible contaminants but have considerable drawbacks from the viewpoint of sanitation. It is a known but disregarded fact that painted surfaces in a room never can be completely diffusion tight. Also during the application of the paint layer craters and pores arise, and when the paint is aged, cracks arise. Additionally, the equipment in the room require that screws, nails, pipes, cables, ventilation ducts, etc., be attached to and brought through the painted surfaces.
Food industries as a rule have a high air humidity. The vapour pressure in a room as a rule is higher than in the surrounding ceilings, walls and floors. Consequently a diffusion of vapour occurs in all openings in the painted coating of the surface (also microscopical), during which the vapour condenses in the wall behind the coating of the surface. The condensed vapour which is transferred into a liquid state cannot in the same easy way move back through the tight coating of the surface as the vapour pressure in the room drops. The walls in rooms with a high air humidity as a rule contain an excess of humidity. This humidity makes a good condition for the growth of micro-organisms and in humid locations this growth behind the paint layers is a problem.
The rooms are daily, i.e., cleaned floors, walls and equipment are washed with a high pressure washer, after which the surfaces, which are to be kept free from micro-organisms, are treated with a sanitizer. During this sanitation the major part of the sanitizers which are sprayed upon walls and ceilings quickly flow away and evaporate from the surface. As the sanitizers only are active in a liquid state, the time in which they affect the micro-organisms is proportionately short and the efficiency consequently will be very low. Besides, the sanitizer will only reach the micro-organisms on the outside, whereas micro-organisms located behind the coating are protected. The surface thus is re-infected not only by micro-organisms in the air in the room but above all by micro-organisms remaining on the back of the paint layer. When the activity of the sanitizer has ceased, the micro-organisms penetrate from the growing locations on the back of the paint layer, which explains why the visible or measurable re-infection sometimes will be surprisingly quick. The re-infection often takes place in a shorter time than 24 hours after the sanitation. This is a problem as most industries have difficulties in carrying out more than one sanitation every 24 hours.
Porous materials traditionally have been regarded as completely unsuitable in rooms with high demands on hygiene. They are regarded as difficult to clean, attracting contaminants and micro-organisms and a good growing base for bacteria, mould, algae, fungi etc.
During laboratory tests and full-scale tests it has now surprisingly been proved that certain types of porous paints have a considerably better resistance to micro-organisms than stainless steel plate. Tests also surprisingly have proved that these types of porous materials are easier to sanitize than corresponding smooth surfaces. Such a porous material is described in the Swedish Patent Publication SE-C-387 681, by which it is also known to prevent or lower the presence of condensate on a surface with a layer of a porous composition of materials including granules with adsorbing and desorbing qualities. This composition of materials also has good heat insulating qualities, which means that a layer of this composition maintains a little higher temperature than a corresponding smooth surface in one and the same room. As a consequence, the porous composition of materials do not attract dust and contamination from the air to the same extent as a smooth surface.